Download chapter 15 - Doral Academy Preparatory

CHAPTER 15
Theory of
Evolution
Charles Darwin
• Charles Robert Darwin
• Born February 12 1809 –
April 19 1882)
• He was an English Naturalist.
• In 1830 Darwin took a trip
around the world on a ship
called the HMS Beagle where
he made many observations
and went on to form one of
the most important theories
in biology.
The voyage of the Beagle
• In December 1831, the British ship HMS Beagle set sail from
England on a five year trip around the world.
• Darwin was
on board as a
Naturalist
• His job was
to learn as much
as possible about
the living things
he saw on the
voyage.
Darwin’s Observations
• Darwin made many observations along his stops on
the Beagle
• Darwin's observations included the diversity of
living things, the remains of ancient organisms, and
the characteristics of organisms on the Galapagos
Islands.
Darwin was amazed by the tremendous diversity of
living things. Scientists now have identified more
than 1.7 million species of organisms.
The Galapagos Islands
• In 1835 the Beagle reached the
Galapagos Islands, where Darwin
observed many unusual life forms
on these small islands such as
giant tortoises and giant iguanas.
•
When Darwin returned to
England, he compared organisms
to organisms that lived
elsewhere. He also compared
organisms on different islands in
the Galapagos group.
• He was surprised by some of the
similarities and differences he
saw.
• Darwin found many
similarities between
Galapagos organisms and
those in South America.
However, there were
important differences.
• The Iguanas on the Islands
had large claws that allowed
them to grip slippery rocks
while the iguanas on the
mainland had smaller claws
to climb trees.
• Darwin was also fascinated
in particular by the land
tortoises in the Galápagos.
• Giant tortoises varied in
predictable ways from one
island to another.
• The shape of a tortoise's
shell could be used to
identify which island a
particular tortoise
inhabited.
Adaptations
• Like the tortoises, the finches on the Galapagos
Islands were noticeably different from one island to
the next.
• The most obvious difference on the Finches was their
beak size and shape.
• Darwin proposed that each species of finch had a
different size and shaped beak to suit its
environment. This is an example of an Adaptation.
• An Adaptation is a trait that helps an organism
survive and reproduce.
Evolution
• Darwin wanted to understand the different
adaptations of organisms on the Galapagos
Islands.
• He hypothesized that the species gradually
changed over many generations and became
better adapted to the new conditions.
• The gradual change in species over time is
called EVOLUTION.
Lamarck’s Ideas on Evolution
• French biologist jean Baptiste Lamarck (17741829) also supported the idea that species
change over time but proposed a different way to
explain HOW evolution happens.
• Lamarck proposed that individuals could acquire
traits during their lifetime as a result of
experience or behavior, then could pass on those
traits to offspring. Lamarck called this idea: the
inheritance of acquired characteristics.
• This idea is no longer accepted by scientists
Descent with modification
• Darwin used the phrase descent with
modification to describe the process of
evolution.
• Descent with Modification-Each living organism
has descended, with changes from other species
over time
• Common Descent- were derived from common
ancestors
• Ex: Darwin's finches
Natural Selection
• In 1858, Darwin and Alfred Russell Wallace, each
proposed an explanation for how evolution could
occur in nature.
• Darwin proposed that evolution could happen by
natural selection.
• Natural selection is the process by which individuals
that are better adapted to their environment are
more likely to survive and reproduce than other
members of the same species.
Darwin identified factors that affect Natural
Selection:
• 1. Overproduction: Most species produce
many more offspring that can possible survive.
• 2. Genetic Variations: any difference between
individuals of the same species.
• 3. Struggle to survive: because resources are
limited, members of a species must compete
with each other to survive.
• 4. Selection: Darwin proposed that over a long
time, natural selection can lead to change.
Helpful variations may gradually accumulate in
a species while the unfavorable ones
disappear.
• Over time, natural selection results in changes
in inherited characteristics of a population.
These changes increase a species fitness in its
environment
Evidence of Evolution
• The Fossil Record
• Geographic Distribution of Living Things
• Homologous Body Structures
• Similarities in Early Development
Evidence for Evolution:
• The Fossil RecordLayers show change
* Different organisms
lived at different times
* Species have differed
in a gradual sequence
of forms over time
(transitional species)
Evidence for Evolution
• Vestigial organs-organs that serve
no useful function in an organism
• i.e.) appendix, miniature legs, arms
Evidence for evolution: Biogeography
• Geographic Distribution of Living Thingssimilar environments have
similar types of organisms
* The model of Descent with
modification provides an
explanation for these
patterns of distribution.
ANATOMY & EMBYOLOGY
• Homologous Structures-structures that
have different mature forms in different
organisms, but develop from the same
embryonic tissue. (similar in structure and
function AND have a common ancestry in
evolution)
• Analogous structures- closely related function
but do not derive from the same ancestral
structure. (similar function but
have a different evolutionary origin)
Similarities in Early Development
Convergent & divergent Evolution
• Convergent evolution is the process by which unrelated or distantly
related organisms evolve similar body forms, coloration, organs, and
adaptations.
Wxample: Convergent evol: WINGS of insects, birds and bats. (thes are also
called analogous structures).
• Divergent evolution occurs when a group from a specific population
develops into a new species. In order to adapt to various environmental
conditions, the two groups develop into distinct species due to
differences in the demands driven by the environmental circumstances.
Adaptive radiation is a process in which one species gives rise to multiple
species that exploit different niches in the environment. The ecological
niches exert the selection pressures that push the populations in various
directions. On the various Galapagos islands, finch species have become
adapted for different diets: seeds, insects, flowers, the blood of seabirds,
and leaves.
Divergent evol: Wings of a bat, the humam forearm and fingers,the flipper
of a whale ,wing of a bird , foreleg of horse.
These are also known as homologous structures.